Ever locked the keys in the c ar?
If you lock your keys in the car and the spare keys are home,
just call someone on your cell phone who has another set.
Hold your cell phone about a foot from your car door and
have the other person at your home or wherever press the
unlock button, holding it near the phone on their end.
Your car will unlock. Saves someone from having to drive
your keys to you. Distance is no object. You could be
hundreds of miles away and if you can reach someone who
has the other "remote" for your car you can unlock the
doors (or the trunk!).